The use of double panes of glass and even triple panes of glass in order to provide insulation against heat and noise is well known. Such windows comprise two or more parallel panes of glass, usually mounted in an elastomeric material such as rubber, for example. That is to say, a strip of rubber material is disposed between the panes of glass at their edges, the rubber on the outside of said edges and below said edges. Means for compressing the rubber so as to seal the glass panes therein and prevent air from leaking into or out of the space between the panes is also provided.
In principal, the idea is extremely simple, however in order to be effective as an insulating device, it is necessary that the dead air space between the panes of glass is effectively sealed. Not only is the insulating value of such windows dependent upon the maintenance of the tight seal, but in addition, visibility also depends upon it. If moisture condenses on the inner surface of the glass, or if a film of grease or dirt accumulates thereon, visibility will obviously be adversely affected if not altogether destroyed. Since it is often impractical to clean the surfaces, it is clear that an effective type seal is vital.
A number of attempts have been made from time to time to provide a satisfactory solution of the problem. These have in general involved the use of rubber sealing strips such as gaskets, with various means for compressing the gaskets against the panes. Experience, however, shows that such constructions do not consistently provide sufficiently uniform pressure to provide an effective air-tight seal when subjected to conventional manufacturing techniques, particularly in wooden sash constructions.
The use of a conventional rubber sealing strip in the normal way, that is, without special efforts to achieve uniform compression, substantially reduces the circulation between the ambient air and the space between the panes. One result is thus that the insulating effectiveness may reach a reasonably good level. Another is that the accumulation of dirt between the panes is retarded; however, when it accumulates, the situation is just as unsatisfactory as the case of an ordinary storm window. If humid air gets into the space between the panes, and the ambient temperature drops, condensation of moisture occurs between the panes and, since the circulation between the ambient air and the space between the panes is slow, the window may remain "fogged" for very substantial periods of time. Thus, in order to decrease the dirt problem, one finds that one has introduced condensation problems which are quite detrimental to good visibility.
Various forms of factory sealed windows when maintained sealed as by fused metal or glass offer high quality insulation. Where pressure elastomeric gasket seals or flexible adhesive seals are provided, the dirt and condensation problem is minimized but still exists. The difficulties with these windows are the extremely high cost, high insurance cost, and expense and difficulty of repair and replacement. The fact that factory fabricated insulating windows can be purchased only in certain specific standard sizes also places limitations in design, especially when curved windows are involved.
The fact that such expensive solutions have nevertheless found very substantial commercial success clearly indicates that the problem itself, that is obtaining good insulating quality without visibility impairment, is a pressing problem and a problem of great commercial importance, and one for which no obvious answer exists.
Thus, there remains a problem of providing a seal as good as presently possible only with factory fabricated insulating windows, which is at the same time inexpensive, readily adapted to any size or shape of window including curved windows, and which can be installed and repaired at the job site instead of requiring factory fabrication.
Of course, air-tight seals are well known in technology, but the problem in connection with the insulating windows is to obtain a seal which is not only effective, but also extremely simple in design and installation and extremely low in cost. Complicated construction may make excellent air-tight seals for scientific and industrial apparatus, but have no place in the construction of buildings, or in vehicles such as automobiles, buses, trains, and airplanes, for simplicity is required.
The difficulties which must be overcome in the solution of this problem include the following:
1. Considerable force must be necessary to make a tight seal, but glass panes must not be broken nor stressed so that the glass panes might break upon a temperature or atmospheric pressure change of additional stress.
2. It is not sufficient to provide an excessively large force at some points and inadequate force elsewhere. "Averages" are not what counts here, but rather a uniform seal around the peripheral inner edges of the adjacent surfaces of the glass panes.
3. Expansions and contractions caused by temperature variations with seasonal changes and by pressure variations with changes in elevation, for example during shipment, must be accounted for without causing breakage on one hand and/or air leakage on the other.
Heretofore, pressure variations between the gas within the space between the lights of a double glazed window and atmosphere as caused by temperature changes or changes in atmospheric pressure have been compensated to reduce the pressure differential across the seals between the lights by providing an auxiliary chamber containing a fixed amount of gas which is at the pressure within the space and is varied in volume to match or approach atmospheric pressure. Larkin U.S. Pat. No. 1,852,661 of Apr. 5, 1932 for "Show Case Refrigerator" discloses sylphons exterior of the double glazed windows of the case and in gas flow communication with the space between the lights so that they expand and contract to compensate for differences in pressure between the interior and exterior of the space. Miller et al., U.S. Pat. No. 2,015,808 of Oct. 1, 1935 for "Double Window Construction" discloses a frame including a cavity containing a tube of thin metal or rubber which may be collapsed and expanded when varying air pressures are applied to the unit. The prior art has also attempted to eliminate the problem of fogging between lights of a hermetically sealed window or transparent panel which is double glazed by introducing dry gas in the space between the lights and/or by including a desiccant in a container in gas communication with that space. Lenhart U.S. Pat. No. 1,913,205 of June 6, 1933 for "Antifogging Device" shows a tray of desiccant screened from but in gas flow communication with the space between lights of a double glazed window. Alternatively a number of patents disclose valves providing admission of gas to the space between lights of double glazed windows and suggest the temporary connection of sources of dry gas for drying and flushing such space. Typical of these U.S. Pat. Nos. are:
1,495,948 -- Carney -- May 27, 1924 PA1 1,851,515 -- Hunt et al. -- Mar. 29, 1932 PA1 2,009,142 -- Marsh -- July 23, 1935 PA1 2,117,581 -- Stoneback -- May 17, 1938 PA1 2,756,467 -- Etling -- July 31, 1956 PA1 2,880,475 -- Mills -- Apr. 7, 1959
Leaks in the units of the prior art having gas drying arrangements have resulted in the admission of sufficient moisture to exhaust the drying capabilities of the desiccant in those units containing a desiccant and the ultimate fogging in the interior of the window. These leaks have been attributed to the pressure differentials between the interior and exterior. In Summers U.S. Pat. No. 2,083,622 of June 15, 1937 the concept of a pressure equalization mechanism combined with a drying medium is disclosed for a double walled panel which in some embodiments is of transparent material. The combination of Summers is cumbersome and does not lend itself to application to conventional windows. Further, if some leakage of moisture into the system does occur the desiccant can be exhausted with a resultant failure of the system.
A replaceable desiccant supply has been proposed for double glazed windows. In Fox U.S. Pat. No. 2,088,738 of Aug. 3, 1937 for "Double Glazed Window" a detachable casing containing desiccant is screw coupled into a cavity in the face of the window frame which is in gas flow communication with the space between the window lights so that it can be replaced when the desiccant is spent. However, this casing protrudes from the window frame and offers an unsightly obstruction. Further, it is a dead end to the gas conduit from the window enclosure with no circulating means and therefore offers only limited access to the gas within the enclosure.
McCurdy et al. U.S. Pat. No. 3,685,239 of Aug. 22, 1972 for "Hermetically Sealed Double Glazed Window Unit and Method for Sealing Same" discloses a rechargeable desiccant chamber in the wall of a window frame wherein a lower port can be opened to withdraw spent granular desiccant and an upper port through which a new charge of desiccant can be introduced. Screw plug seals are disclosed for each port.